Depends on if they'll have dedicated graphics this time. If they do I can easily see another 8GB with 8GB more on the GPU. 32GB total would be fine for any usecase in the next 5 years but we wouldn't want to have that in a console. So 16 seems like a natural evolution. Maybe 24GB if they want to flex their muscles towards their competitors.

First will people get off this idea that phones cost $600 - $1,000. They are $250 devices that you are getting massively price gouged on.

Then lets talk the idea that we will never need more than X amount of RAM. This has been debunked time and time again. Why don't games use massively more on PC, because games are built to the PS4 and XBO. Whatever the PS5 and XB4 have, game development will shift to. If PS5 and XB4 have 32 core CPU's and 128GB of RAM, then software will be built for 32 cores and 128GB of RAM.

As for what the PS5 will likely have. Well, 128GB is not looking like it will happen. It doesn't look like Sony is going to stick with PS4 for another 4 years, so PS5 is going to end up being the smallest jump in the history of the platform.

Here are the three most likely options:

(8) 2GB Modules on a 256bit Bus (16GB)
-This is the bare minimum. It is cheap from day one, but offers little in the way of future proofing, and price reductions.

(12) 2GB Modules on a 384bit Bus (24GB)
-This would give them a little more distance from PS4 Pro and XBO X, and make things feel like somewhat of a leap. This would be another option with little room for future price reduction, but it would future proof the system a little.

(16) 2GB Modules on a 256bit Bus (32GB)
-This is the best option IMO. This would give them a leap between the Pro and X that would be very noticable. It would allow them to take advantage of 4GB GDDR6 Modules, and cut the cost half way through the life cycle. It would offer decent future proofing.

Bonus Option

(24) 2GB Modules on a 384bit Bus (48GB)
-This is the insane option. This would give them close to a generational leap, and offer an incredible increase in througput as well. It would also allow them to make a giant cost reduction when 4GB GDDR6 Modules hit the market. This would set the console up for a really good decade long run.

I am hoping for either the 32GB of 48GB options. Then I would love to see the PS5 Pro and XB4 X use the 4GB Modules to double up either offering 64GB or 96GB. I don't see any reason why they should go with 16 or 24GB, because they offer to little gain, and no cost reduction solutions during the generation.

Id say 16 to 24gig if its GDDR5 and 12 to 16gig if its GDDR6+.

16GB for PS5  & 32GB for PS5Pro 

16 GB will be fine. Most games these days only want 8 GB.

That's not quite true nowadays. The iPhone X and the Samsung S9 Plus cost nearly $400 to produce, and have 3-6 GB of RAM - less than current consoles. Their RAM is very pricey, actually, with each GB costing about $6 to $8. Even assuming prices fall 15 - 25% after the end of shortages as some predict, that's still quite hefty, considering more RAM means also a more complex motherboard.

https://pocketnow.com/samsung-galaxy-s9-plus-production-costs-note-8-iphone-x

https://www.techwalls.com/production-costs-of-smartphones/

I don't think there is such a thing as "future proofing", as well. Consoles are whatever affordable hardware there is when they launch, and that's it. The PS3 tried to be the only exception and even then it was supposed to be a much more insane and costly - 2 GB of split RAM, lots of USB and ethernet ports etc. and it still ended up with poorer-looking games than the more modestly and smartly built X360.

Besides, it doesn't seem like gaming PCs are as bound to console specs as you would believe. Back in 2010, the average PC RAM was some 3 GB already, six times more than consoles back then. Nowadays, it's a mere 9 - 10 GB, not even a fifth more than consoles. You can look for news about the Steam Statistics, if you want to check it.

I would like for the next consoles to have 32 GB of RAM, as well, but to expect sixteen 2 GB modules to cost about the same as Sony spent back on the original PS4 seems too opmistic, even more so if we want to see proportionally more improvements on CPU etc.

256 the PS3...

32 GB DDR6

The extra bandwidth on offer has an effect on fillrate which assists with texturing.

One of the easiest and fastest upgrades you can do to a PC is to upgrade it yourself.
It takes a couple minutes tops you know.

512MB.

I wanted to vote 64GB, but it wasn't an option.